PRODUCT DATABOOK 1996/1997
LX1664/1664A, LX1665/65A
D
UAL
O
UTPUT
PWM C
ONTROLLERS
P
R O D U C T I O N
WITH
5-B
IT
DAC
D
A T A
S
H E E T
B I L L O F M AT E R I A L S
Ref
C
1
C
2
C
7
, C
9
C
3
C
4
C
8
C
5
L
1
L
2
Q
1
Q
2
Q
3
R
5
, R
6
R
1
U1
Total
Description
LX1665 Bill of Materials
(Refer to Product Highlight)
Part Number / Manufacturer
MV-GX Sanyo
MV-GX Sanyo
MV-GX Sanyo
SMD Cap
SMD Cap
SMD Cap
SMD Ceramic
HM0096832 BI or equivalent
IRL3102 International Rectifier or equivalent
IRL3303 International Rectifier or equivalent
IRLZ44 International Rectifier or equivalent
SMD Resistor
IRC OARS-1 or PCB trace
LX1665CDW Linfinity
Qty.
4
2
2
1
1
1
1
1
1
1
1
1
2
1
1
21
1500µF, 6.3V capacitor
1500µF, 6.3V capacitor
330µF, Electrolytic
0.1µF
390pF
680pF
1µF, 16V
2.5µH Inductor
1µH Inductor
MOSFET
MOSFET
MOSFET
Resistor
(See Table 6 for values)
2.5mΩ Sense Resistor
Controller IC
USING THE LX1664/65 DEVICES
The LX1664/65 devices are very easy to design with, requiring
only a few simple calculations to implement a given design. The
following procedures and considerations should provide effec-
tive operation for virtually all applications. Refer to the
Appli-
cation Information
section for component reference designa-
tors.
TIMING CAPACITOR SELECTION
The frequency of operation of the LX166x is a function of duty
cycle and OFF-time. The OFF-time is proportional to the timing
capacitor (which is shown as C
8
in all application schematics in
this data sheet), and is modulated to minimize frequency
variations with duty cycle. The frequency is constant, during
steady-state operation, due to the modulation of the OFF-time.
The timing capacitor (C
T
) should be selected using the
following equation:
(1 - V
OUT
/V
IN
) * I
DIS
C
T
=
f
S
(1.52 - 0.29 * V
OUT
)
Where I
DIS
is fixed at 200µA and f
S
is the switching frequency
(recommended to be around 200kHz for optimal operation and
component selection).
When using a 5V input voltage, the switching frequency (f
S
)
can be approximated as follows:
I
DIS
C
T
= 0.621 *
f
S
Choosing a 680pF capacitor will result in an operating
frequency of 183kHz at V
OUT
= 2.8V. When a 12V power input
is used, he capacitor value must be changed (the optimal timing
capacitor for 12V input will be in the range of 1000-1500pF).
L
1
OUTPUT INDUCTOR SELECTION
The inductance value chosen determines the ripple current
present at the output of the power supply. Size the inductance
to allow a nominal ±10% swing above and below the nominal DC
load current, using the equation L = V
L
*
∆T/∆I,
where
∆T
is the
OFF-time, V
L
is the voltage across the inductor during the OFF-
time, and
∆I
is peak-to-peak ripple current in the inductor. Be
sure to select a high-frequency core material which can handle
the DC current, such as 3C8, which is sized for the correct power
level. Typical inductance values can range from 2 to 10µH.
Note that ripple current will increase with a smaller inductor.
Exceeding the ripple current rating of the capacitors could cause
reliability problems.
Copyright © 1999
Rev. 1.2 11/99
11
MICROSEMI [ MICROSEMI CORPORATION ]
